京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17894号 / 工博第3803号 / 新制||工||1582(附属図書館) / 30714 / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 大嶋 正裕, 教授 山本 量一, 教授 宮原 稔 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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This study analyzed the feasibility of using gas foaming to create Poly Lactic-co-Glycolic Acid (PLGA) scaffolds for use as a substrate in bone tissue engineering and set out to determine whether the presence of osteoblasts on these scaffolds enhanced their material stiffness. The process of bone formation involves osteoblasts depositing extracellular matrix and calcifying this matrix with calcium phosphate crystals (Hasegawa et al., 2017) and pits between 30-40μm in diameter on tissue engineering scaffold surfaces have been shown to best promote osteogenic activity in the presence of bone-forming cells (Halai et al., 2014).The scaffolds were determined to contain pits within this 30-40μm range and the ability of osteoblasts to lay down and calcify extracellular matrix on gas foamed PLGA scaffolds was confirmed by the image analysis of inverted optical microscope images of Alizarin Red S-stained scaffold cryosectionsThe presence of osteogenic activity combined with the desired scaffold porosity led us to conclude that gas foaming PLGA scaffolds are a feasible method of scaffold fabrication for bone tissue engineering and allowed us to optimize the gas foaming apparatus as an instrument to be used in further bone tissue engineering experiments at California Polytechnic State University, San Luis Obispo.However, this study failed to determine whether the presence of osteoblasts improved the material stiffness of the PLGA scaffolds due to a lack of statistical significance in compression testing results.

Yes / This work evaluates the efficiency of the aqueous mixture of Methyl Diethanolamine (MDEA) and Diethanolamine (DEA) at various mass concentrations to remove CO2 and H2S from natural gas in an industrial sweetening unit in Fajr Jam Gas Refining Company located in the south of Iran and gives recommendations for modifying the process. The sweetening unit includes absorber and desorption towers, flash drum, lean and rich amine exchanger, kettle type reboiler and a reflux drum. The considered process is simulated by Promax simulator (version 3.2) taking into account operational constraints and sustainability of the environment. The validity of simulation has been evaluated by comparison between simulation results and the plant data. The main objective of this work is the modification of natural gas sweetening unit to achieve lower energy consumption. Thus, the effect of amine circulating rate and MDEA to DEA ratio on steam consumption in the regeneration tower, CO2 and H2S concentration in the treated gas, and the acid gas loadings have been investigated. Therefore, substitution of DEA solvent in the unit with the aqueous mixture of DEA and MDEA is proposed. In the examined cases, the mass concentration of MDEA and DEA lies between 15 and 45 wt% and 0–30 wt%, respectively, with the reference cases having MDEA 0 wt% and DEA 31.6 wt%. The results show that in the proposed cases of alternative mixtures including cases 1 (MDEA15 wt% and DEA 30 wt%), 2 (MDEA 20 wt% and DEA 25 wt%), and 3 (MDEA 25 wt% and DEA 20 wt%) the amount of reduction in amine circulation rate are between 11.1%v/v and 19.4%v/v compared to the original amine circulation rate. Likewise, steam consumption decreases between 24.4 %wt/wt and 27 %wt/wt. Influence of anti-foam injection for the different cases were also studied and it was found that anti-foam with the concentration of 5000 ppmv is more suitable for the optimum operation and is a more cost effective.

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<p>Recent experiment in our laboratory demonstrates that an increase in slag foamingwith carbon injection rate is limited by slag volume. The current work has identified arelationship between foam height, carbon injection rate and slag volumes, whichpredicts the critical injection rate above which foaming become inefficient. Theprediction of critical injection rate employs an extension of understanding mechanismof bubble movement in the foam by estimating average/steady-state bubble size andwall thickness. The carbon gasification model developed in our laboratory by King etal., which has been extended to include greater consideration of gas bubble burstingwhen to predict bubble size, and further improvement for calculating how fast bubblecan burst instantaneously in carbon-gas-slag halo system, has found that has importantinfluence on the predicting foaming parameters in King’s model, which is crucial taskfor continuous development in future.</p> / Master of Applied Science (MASc)

Interest in high-pressure and supercritical fluids as physical blowing agents for polymer foaming is driving a renewed need for the fundamental understanding of polymer thermophysical and rheological properties in the presence of dense fluids. In particular, carbon dioxide is often studied as a physical blowing agent because of its readily accessible critical point (31.1 ℃ and 73.8 MPa) and relatively high solubility levels in polymer materials. The basic principle involved is to dissolve the supercritical fluid in the polymer at high pressures and then impose a pressure reduction to initiate bubble nucleation and growth. The outcomes depend on the thermophysical and rheological properties of the polymer under the prevailing process conditions in the fluid. The present dissertation explores the high-pressure characterization and foaming of thermoplastic elastomers and seeks to link polymer thermophysical and rheological properties to polymer foaming outcomes with carbon dioxide as a physical blowing agent. A major focus of this dissertation has been the development of novel high-pressure characterization techniques to understand polymer behavior at high pressure. These techniques include (1) high-pressure torsional braid analysis (HP-TBA), (2) magnetic suspension balance (MSB), and (3) unique high-pressure batch foaming cells. HP-TBA allows for the assessment of the depression in thermal transitions (Tg and/or Tm/Tc) and the changes in rheological properties like modulus or rigidity of polymer systems exposed to carbon dioxide. MSB provides for the assessment of the amount of carbon dioxide that sorbs into a polymer material at a given temperature and pressure. Unique confined foaming strategies have been developed to translate information learned from batch-scale experimentation to practical industrial applications. The polymer systems of interest are thermoplastic elastomers including poly(ethylene-co-vinyl acetate) (EVA) and poly(ethylene-co-vinyl acetate-co-carbon monoxide) (EVACO). These materials find use in numerous commercial applications including adhesives, compatibilizers, and foams. Their foams are noted to undergo significant degrees of expansion followed by unfavorable post-foaming collapse. In the first part of this study, the foaming of neat EVACO and EVA with carbon dioxide was explored. The blending of these polymers was then explored to regulate foam expansions and control the pore morphology development. The foamability of the polymers and their blends was explored under both isothermal and gradient conditions to assess the temperature effects on foaming outcomes at a given pressure. In the second part of this study foaming of EVACO was explored in relationship to the depressed thermal transitions of the polymer in the presence of carbon dioxide. Accompanying the depressed melting transition is a sharp reduction in the modulus or rigidity of the polymer material. By studying foaming outcomes near the melting transition rational windows for foaming exploration can be evaluated to generate foams that display more favorable bulk foam densities and minimal foam collapse. This part demonstrates that linking foaming conditions to the relative rigidity or melt strength of EVACO in carbon dioxide allows for the determination of the lower pressure where foaming will occur and the upper pressure beyond which further foam density reductions are not significant. The third part of this study explores the foaming of EVACO with carbon dioxide under batch, confined foaming conditions where the foam expansion is restricted in order to again control the foaming outcomes and prevent foam collapse. A practical question is the scale-up of batch foaming processes which likely will be conducted with injection molding or extrusion type processes. Studying batch foaming in confinement allows for a better understanding of the factors that may affect foam development that may be more readily translated to industrial practice. The fourth part of this study examines the role of crystallinity and block copolymer composition in altering the polymer behavior in carbon dioxide. Several EVACO polymers with varying ethylene, vinyl acetate, and carbon monoxide content have been explored to study how block copolymer composition affects the thermophysical and rheological properties along with the sorption of carbon dioxide at high pressure. / Doctor of Philosophy / Polymers, colloquially referred to as plastics, are used as the materials to generate foams like the sole of a tennis shoe or the Styrofoam coffee cup on your desk. Currently, these materials are made using environmentally damaging and potentially health hazardous chemicals that are gradually being phased out by global regulations. Producing polymer foams, or foaming, using compressed carbon dioxide is a more environmentally favorable process to generate porous or "foamed" materials. It is crucial to understand how the polymer behaves in a high-pressure environment with gases such as carbon dioxide to manufacture these materials. Several unique instruments were developed to understand polymer behavior in carbon dioxide, allowing for insights into polymer material behavior at high pressure. This information can then be translated into selecting temperature, pressure, and saturation conditions from which to generate polymer foams. The polymers of interest are rubbers that display elastic behavior like a classic rubber band. They are of interest in athletic equipment, tennis shoes, or other areas where repetitive compression and recovery properties are essential. In the first part of this study blending of two polymer systems was explored to see how blending alters foaming outcomes. In the second part, foaming was explored in relationship to the material behavior of the polymer in the presence of carbon dioxide. Specifically, this part involves the study of foaming near the melting transition, which is the transition where the polymer material loses its ordered structure. Studying foaming outcomes near the melting transition allows rational windows for foaming exploration to be evaluated to generate foams that display more favorable bulk foam densities and minimal foam collapse. The third part explores the foaming of polymers with carbon dioxide under batch confined foaming conditions where the foam expansion is restricted to control the foaming outcomes again and prevent foam collapse. A practical question is the scale-up of batch foaming processes which likely will be conducted with injection molding or extrusion type processes. Studying batch foaming in confinement allows for a better understanding of the factors that may affect foam development that may be more readily translated to industrial practice. The fourth part examines a series of polymers that display different degrees of elasticity. This study allows for understanding how elasticity may impact foaming outcomes like the collapse observed after the foam is generated.

In the steel industry, slag foaming plays a crucial role in many steel processes, given its positive impact on the thermal efficiency of the furnace and its life span. However, excessive foaming causes an overflow in the converter known as “slopping”. Slopping hinders the effectiveness of the processes, especially with the complex and unpredictable foaming rate. This problem occurs mainly in the BOS-processes and after melt tapping to the ladle furnace. The goal of this study is to test and relate a new foaming control system, by blowing a gas (nitrogen or argon) on the surface of the melt to suppress the foam. Firstly, the foaming index of the provided industrial heats for a general LD converter (21 heats) and Outokumpu’s ladle furnace (31 heats) were calculated to find which heat is most likely to slop. Then, a series of experiments were performed to investigate the new foam controlling system’s reliability using a cold model. The results demonstrated that blowing argon instead of nitrogen from the top nozzle suppresses the foam more effectively, which can be attributed to its higher density. Additionally, the optimal argon flow rate required to suppress the foam in worst-case slopping scenarios in the LD converter and the ladle furnace were 874 and 221 m3/min respectively. The provided data further supports the efficacy of this slopping prevention technique, in theoretical and practical aspects. / I stålindustrin spelar slaggskumning en avgörande roll i många stålprocesser, med tanke på dess positiva inverkan på ugnens termiska effektivitet och dess livslängd. Överdriven skumning orsakar emellertid ett överflöde i konvertern som kallas "utkok". Utkok hindrar processernas effektivitet, särskilt med den komplexa och oförutsägbara skumningshastigheten. Detta problem uppstår främst i BOS-processerna och efter tappning till skänkugnen. Målet med denna studie är att testa ett nytt kontrollsystem genom att blåsa en gas (kväve eller argon) på smältytan för att slå sönder skummet. Först beräknades skumindexet för de tillhandahållna industriella chargerna för en allmän LD (21 charger) och Avestas skänk (31 charger) för att hitta vilken charge som har störst risk för utkok. Därefter utfördes en serie experiment för att undersöka det nya skumstyrsystemets tillförlitlighet med hjälp av en kall modell. Resultaten visade att blåsning av argon istället för kväve från det övre munstycket undertrycker skummet mer effektivt, vilket kan hänföras till dess högre densitet. Dessutom var den optimala argonflödeshastigheten som krävdes för att undertrycka skummet i värsta fallet i LD och skänkanläggningen 871 respektive 221 m3/min. De tillhandahållna uppgifterna stöder ytterligare effekten av denna förebyggande teknik, i teoretiska och praktiska aspekter.

This thesis reports a fundamental study on microwave assisted moulding (MAM), a novel technology where expandable starch based pellets made from extrusion are expanded within a mould cavity into blocks using microwave heating. Foamability or degree of expansion of starch-based pellets during microwave heating was studied comprehensively in terms of: the variation of raw natural materials, the extrusion conditions, the additives and the preconditioning of pellets before foaming. The expansion behaviour, foamed cell structures and mechanical properties of expanded pellets were characterized together with the characterization of microstructure of the extrudate materials and physical properties. Characteristics in microwave assisted moulding of the expandable pellets were then studied in terms of: the interfacial bonding and fusion between foamed pellets, the achievement of uniform heating through a moulded block, the loading of pellets and mould filling during foaming. It has been found that the degree of free expansion during microwave heating of the starch-based pellets is dependent on the degree of cook of starch during extrusion, the better the distructurization of the native starch granules, the higher the foamability in microwave heating. The maximum expansion ratio achieved in this work is 14, corresponding a foam porosity of 93%. Hydrophilic additives such as PYA and glycerol have adverse effect on the foamability due to combination effects of the melting point of the materials, degree of cook of starch in the pellets and water molecular mobility during foaming. Nucleation agents such as talc powder can refine cell structure of the foams and enhance elastic modulus, strength and energy absorption during compression. Addition of salts enhances microwave heating rate, expansion ratio and plasticization of the foam. Foamed blocks can be made using the MAM technology by adequate mould material, pre-treatment of the pellets, and control of initial loading in the mould cavity. This study paved the way for further development of the MAM technology for moulding of starch-based foams.